GX460 Repairs Questions - Feedback Needed

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GXHowie

GXHowie

Joined
Dec 2, 2024
Threads
5
Messages
18
Location
Carlsbad, CA
Background
  • I’m reaching out for much needed and appreciated suggestions and feedback on what the Techs are suggesting for my GX460 “P0328 Knock Sensor Code” problem.
  • My Independent Service Tech, after consulting with the Lexus Dealership, is recommending replacement of all 4 Knock Sensors (2 Left Side, 2 Right Side) to resolve the problem.
  • The Lexus Dealer is even suggesting replacement of the EGR Valve, “because the EGR Valves are known to be sensitive, and easily damaged during these repairs, and should be replaced”. My Independent Service Tech disagrees with the idea that the EGR Valve should be replaced, but believes at a minimum both Knock Sensors on the High Bank side should be replaced, if not all 4.
  • All thoughts or suggestions would be much appreciated! 🙏

Questions

Question 1 - What are the chances that all 4 Knock Sensors are bad?

Ih8mud, and other Toyota forum research, suggests it highly unlikely that all 4 sensors fail simultaneously, but highly likely that rodent problems and chewed up harnesses could be the problem.

My Tech suggests that if they find its just the harness that is chewed up, they will replace only the harness.

Any feedback on all this?

Question 2 - What other Maintenance should I consider while the Techs are in there doing Knock Sensor/Harness replacement, my GX460 has 90K miles?

Some folks have suggested that “more work should be done, while they are in there, for preventive maintenance and cost savings” e.g. Replace all Knock Sensors, Replace Valve Cover Gaskets, Replace Spark Plugs.

This sounds reasonable, I had the Water Pump and Serpentine Belt replaced last year.

What should be on the list of maintenance done during this project?

Question 3 - Is it OK to drive out to the Borrego Cleanup #3 Trip with this Error Code, or should I get repairs first? As, they may not be done with repairs this week.

Many Thanks - Howie
 
Break it down into Pieces. Move the top the bottom locations and see if the code follows. Then you know not all are bad. Never heard of a Knock sensor going this early. Spark Plugs I change every 50k = Preventive maintenance Driving to Borrego you should be fine. Clear your codes and see where they pop up either again or some where else. Call me and I'll bring out my OBD2 reader....951-385-3170
 
The odds all 4 being bad are astronomically low. Shops don't like people coming back for the same issue over and over so they assume one is bad, the others are old, replace them all and call it a day. There is piece of mind in that but it costs. Any shop with a mobile oscilloscope scope could probe the sensors and actually see which is bad. If you have a harness issue, replacing sensors won't help at all. I think for me it comes down to root causing the issue. Are they saying it will cost more in tech time to troubleshoot than just replace the parts? It does sound like your tech did his homework so no reason I can see not to trust that tech.

I haven't gone into that engine. However, given that we sometimes go way off grid, I err on the side of caution and replace parts that are either hard to get to or already disturbed in the repair process. If they have to remove stuff that covers most of the labor of other hard to get to small parts, I would replace them especially if the labor is a lot more than the part. Still, 90k is not a lot, I'd likely pass on the EGR unless it's a known early failure. Interestingly, too little EGR will lead to more spark knock which will cause the engine to take remedial actions. However, you should be getting an EGR temp fault and it sounds like you are Ok there. If you are still on original plugs, etc... I'd change them at 90K.

You can drive with that error as long as the drivability is tolerable. When engines experience predetonation (well below the hearing threshold...) they retard the timing and can also enrich the mixture. In fact, EPA allows for those things to avoid engine damage under severe conditions even though they increase emissions. If you aren't experiencing drivability issues, most likely you have only 1 bad sensor and the engine is able to operate on "safe" settings using the other 3, like slightly retarded timing, to ensure no damage occurs. I have had knock issues on past vehicles that were so bad the engine was stumbling and falling on its face so to speak. If that were the case you wouldn't want to drive it due to it just being plain miserable to operate. If it's running fine I wouldn't worry, do the trip, then have it addressed.

Frank
 
I was going to suggest rodents damaging the knock sensor harness. They like like to nest on top of the engine under the plastic cover and the wiring is soy-based which rodents like to chew on (so I've read).

Consider resealing the valley plate cover while you are in there. Most of it is labor and you'll have most of that apart when replacing the knock sensors. Check the 200 series section for some threads on this. Those are for the 3UR but same issue applies to the 1UR as far as I know.

cc93cruiser

Thread 'Kind of "Mystery" Coolant leak back of engine (heat exchanger valley leak)'

Hey guys, I had another thread going on on my 09 Lx puking out coolant from what I thought was the waterpump.. But after taking wheels off and a bunch of other plastic crap off of the front of engine (more than I want to remember) waterpump area is completely dry and is coolant drip free (no pink crap anywhere). It seems that all the dripping of coolant is from passenger side control arm back.. there's a lot! After further inspection I seen that the dripping starts from top of tranny hump all the way in the back of motor... There are a bunch of coolant and heater hoses rubber and metal...
 
KTP said:
Break it down into Pieces. Move the top the bottom locations and see if the code follows. Then you know not all are bad. Never heard of a Knock sensor going this early. Spark Plugs I change every 50k = Preventive maintenance Driving to Borrego you should be fine. Clear your codes and see where they pop up either again or some where else. Call me and I'll bring out my OBD2 reader....951-385-3170
Click to expand...
Many Thanks. just added Spark Plugs to the list.
 
elripster said:
The odds all 4 being bad are astronomically low. Shops don't like people coming back for the same issue over and over so they assume one is bad, the others are old, replace them all and call it a day. There is piece of mind in that but it costs. Any shop with a mobile oscilloscope scope could probe the sensors and actually see which is bad. If you have a harness issue, replacing sensors won't help at all. I think for me it comes down to root causing the issue. Are they saying it will cost more in tech time to troubleshoot than just replace the parts? It does sound like your tech did his homework so no reason I can see not to trust that tech.

I haven't gone into that engine. However, given that we sometimes go way off grid, I err on the side of caution and replace parts that are either hard to get to or already disturbed in the repair process. If they have to remove stuff that covers most of the labor of other hard to get to small parts, I would replace them especially if the labor is a lot more than the part. Still, 90k is not a lot, I'd likely pass on the EGR unless it's a known early failure. Interestingly, too little EGR will lead to more spark knock which will cause the engine to take remedial actions. However, you should be getting an EGR temp fault and it sounds like you are Ok there. If you are still on original plugs, etc... I'd change them at 90K.

You can drive with that error as long as the drivability is tolerable. When engines experience predetonation (well below the hearing threshold...) they retard the timing and can also enrich the mixture. In fact, EPA allows for those things to avoid engine damage under severe conditions even though they increase emissions. If you aren't experiencing drivability issues, most likely you have only 1 bad sensor and the engine is able to operate on "safe" settings using the other 3, like slightly retarded timing, to ensure no damage occurs. I have had knock issues on past vehicles that were so bad the engine was stumbling and falling on its face so to speak. If that were the case you wouldn't want to drive it due to it just being plain miserable to operate. If it's running fine I wouldn't worry, do the trip, then have it addressed.

Frank
Click to expand...
Frank - You just made me smile, knowing I can stay on the road til repairs are done, look forward to seeing you guys next weekend!
 
sdnative said:
I was going to suggest rodents damaging the knock sensor harness. They like like to nest on top of the engine under the plastic cover and the wiring is soy-based which rodents like to chew on (so I've read).

Consider resealing the valley plate cover while you are in there. Most of it is labor and you'll have most of that apart when replacing the knock sensors. Check the 200 series section for some threads on this. Those are for the 3UR but same issue applies to the 1UR as far as I know.

cc93cruiser

Thread 'Kind of "Mystery" Coolant leak back of engine (heat exchanger valley leak)'

Hey guys, I had another thread going on on my 09 Lx puking out coolant from what I thought was the waterpump.. But after taking wheels off and a bunch of other plastic crap off of the front of engine (more than I want to remember) waterpump area is completely dry and is coolant drip free (no pink crap anywhere). It seems that all the dripping of coolant is from passenger side control arm back.. there's a lot! After further inspection I seen that the dripping starts from top of tranny hump all the way in the back of motor... There are a bunch of coolant and heater hoses rubber and metal...
Click to expand...
Perfect idea - Valley Plate Cover is added to the list. Its makes it feel better to get a bunch of stuff done, maybe save a few buck that way.
 
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